Watching The Web - Code Poet
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With the theory out of the way, I was just about ready to make my first stab at the code. Since I was told that there are a large number of URLs to be monitored, I decided to use a MySQL database table to store them, in addition to a brief description of each URL. The table I came up with is pretty simple - here's what it looked like:
CREATE TABLE urls (
id tinyint(3) unsigned NOT NULL auto_increment,
url text NOT NULL,
dsc varchar(255) NOT NULL default '',
date datetime default NULL,
email varchar(255) NOT NULL default '',
PRIMARY KEY (id)
);
And here's a sample of the data within it:
mysql> select * from urls;
+----+---------------------------------+----------------+------+--------
+----+---------------------------------+----------------+------+----
------+
| id | url | dsc | date | email
|
+----+---------------------------------+----------------+------+--------
+----+---------------------------------+----------------+------+----
------+
| 1 | http://www.melonfire.com/ | Melonfire.com | NULL |
user@some.domain |
| 2 | http://www.yahoo.com/ | Yahoo.com | NULL |
user@some.domain |
| 3 | http://www.devshed.com/ | Devshed.com | NULL |
user@some.domain |
+----+---------------------------------+----------------+------+--------
+----+---------------------------------+----------------+------+----
------+
3 rows in set (0.00 sec)
Next up, I needed a script
that would iterate through this database table, connect to each of the URLs listed within it, and obtain the value of the "Last-Modified" header - basically, replicate what I did with my telnet client, as many times as there were URLs. Here's what I put together:
<?php
// DB connection parameters
$db_host="localhost";
$db_user="joe";
$db_pass="65h49";
$db_name="db167";
// open database connection
$connection = mysql_connect($db_host, $db_user, $db_pass) or die
("Unable to connect!"); mysql_select_db($db_name);
// generate and execute query
$query1 = "SELECT id, url, date, dsc, email FROM urls"; $result1 =
mysql_query($query1, $connection) or die ("Error in query: $query1 . " .
mysql_error());
// if rows exist
if (mysql_num_rows($result1) > 0)
{
// iterate through resultset
while(list($id, $url, $date, $desc, $email) =
mysql_fetch_row($result1))
{
$response = "";
// parse URL into component parts
$arr = parse_url($url);
// open a client connection
$fp = fsockopen ($arr['host'], 80);
// send HEAD request and read response
$request = "HEAD /" . $arr['path'] . "
HTTP/1.0\r\n\r\n";
fputs ($fp, $request);
while (!feof($fp))
{
$response .= fgets ($fp, 500);
}
fclose ($fp);
// split response into lines
$lines = explode("\r\n", $response);
// scan lines for "Last-Modified" header
foreach($lines as $l)
{
if (ereg("^Last-Modified:", $l))
{
// split into variable-value component
$arr2 = explode(": ", $l);
$newDate = gmdate("Y-m-d H:i:s",
strtotime($arr2[1]));
// if date has changed from
last-recorded date
if ($date != $newDate)
{
// send mail to owner
mail($email, "$desc has
changed!", "This is an automated message to inform you that the URL
\r\n\r\n $url \r\n\r\nhas changed since it was last checked. Please
visit the URL to view the changes.", "From: The Web Watcher
<nobody@some.domain>") or die ("Could not send mail!");
// update table with new date
$query2 = "UPDATE urls SET date
= '" . $newDate . "' WHERE id = '" . $id . "'";
$result2 = mysql_query($query2,
$connection) or die ("Error in query: $query2 . " . mysql_error());
}
}
}
}
}
// close database connection
mysql_close($connection);
?>How does this work? Let's look at that
next.
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